The present invention relates to a control system to provide a speed reference signal to an adjustable speed drive for a laying tube type coiler. The rod, wire or strand is fed to the coiler at a substantially constant speed, while the speed of the coiler tube is alternately increased and decreased as a function of the speed reference, the rod, wire or stand emerging from the coiler being deposited in a receiving basket or carrier in spiraled ring layers.
In the past the speed reference for the coiler was obtained by using a stepping switch to selectively and successively make contact with a plurality of potentiometers, empirically adjusted, to provide a plurality of voltages for generating the periodically varying speed reference signal. The adjustment of the potentiometers is tedious and in addition, installation and maintenance are expensive.
The next step in the art was to use static components, i.e., operational amplifiers. A mathematical analysis of the problem disclosed that the speed reference should be adjusted as a function of the cube of the coiler speed and the square of the rod speed. Ideally then, if the speed were so adjusted, the rod wire or strand would nest in the basket or container in concentric rings one above the other, the symmetry only being broken by necessity when the coiler moved between the projected inside and outside diameters.
In the practical situation it has been found that the rod, or wire did not conform to the predicted classical geometry and instead resulted in irregular configurations. One such irregularity for example is the so-called beehive stacking of the coils, i.e., the outside diameter of the final coils is less than the initial coils. This condition can be prevented in some degree by manual manipulation of the speed reference for the coiler, but on the whole the results are fortuitous and depend on the skill of the operative making the adjustments.
The present invention proposes to produce more predictable and accurate results by the introduction of two additional factors which are algebraically added to the prior art coiler speed parameter to provide the speed reference signal.